In recent years, an optical module in which an optical semiconductor device is mounted on an optical wiring board, has come to be utilized in electronic equipment. The optical wiring board includes a wiring substrate for transmission of electric signals, and an optical waveguide formed on the wiring substrate, for transmission of optical signals.
For example, in Japanese Unexamined Patent Publication JP-A 2000-347051, there is disclosed a mounting board (optical module) comprising a substrate having electrical wiring (wiring substrate); an optical wiring layer formed on the substrate (optical waveguide); an optical component mounted on the optical wiring layer (optical semiconductor device); a pad placed on the optical wiring layer, to which is soldered the optical component; and a via-hole formed so as to pass through the optical wiring layer in its thickness direction, for providing connection between the pad and the electrical wiring.
However, when the optical component is soldered to the pad placed on the optical wiring layer, the interposition of solder between the optical component and the pad placed on the optical wiring layer may result in an increase in the distance between the optical component and the optical wiring layer. Therefore, light that has been emitted to the optical wiring layer from the optical component, or light that the optical component received from the optical wiring layer, is prone to diffusion between the optical component and the optical wiring layer. In consequence, optical signals become susceptible to attenuation between the optical component and the optical wiring layer, which may cause deterioration in signal transmission characteristics of the mounting board.